Piezo-electric oscillator



Feb. 25, 1930. A. L, R. .ELLES PIEZO ELECTRIC OSCILLATOR Filed May ll, 1926 H s, Attorn ey.

Patented Feb. 25, y193() ALvAnaDo L. n. ELLIS, or swamrscofr'r,

MASSACHUSETTS, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK Plazo-ELECTRIC oscILLA'roa Application led Hay 11,

My invention relates to oscillators comprising a piezo-electric element such as a crystal of quartz, or the like, and has for its principal object the provision of an improved mounting which is so constructed as to permit ready assembly and accurateadjustment of the oscillator parts. Further objects are the provisionl of a mounting which permits the electrodes of the oscillator to be readily locked together when the spacing between them hasbeen adjusted and which obviates or greatly minimizes the eiect of temperature changes on the operating characteristics of the oscillator.

It is well known that a piezo-electric element, such as a crystal of quartz or the like, will oscillate at a frequency dependent on its dimensions when subjected to an electrostatic field and that this characteristic of the piezo-electric element may be utilized to predetermine very accurately the frequency vat which current is suppliedv from a source toan output circuit. In order to ensure the -best operation of the piezo-electric oscillator,

it is desirable that the surfaces of the electrodes and the active surfaces of the piezoelectric element be maintained substantially parallel, that the electrode surfaces be accurately spaced from one another, and that means be provided for preventing change in this spacing when it is once adjusted. It a piezo-electric element is inserted between xed'electrodes connected in a suitable circuit, it is probable that this element will oscillate andcontrol the circuit but therel is a possibility that it will not oscillate at all anda probability that it will not oscillate with anything like its maximum effect. The activity of the crystal is a very important matter for the reason that it determines the number of stages required between the input and output circuits. In order to insure the proper operation of the piezo-electric element, it is essential that the element be properly mounted between thefelectrodes.

What takes place ina piezo-electric cell will be readily understood by considering the mechanical coupling of the electrodes and piezo-electric element as the air gap between the element and the electrodes is increased.-

1926. Serial No. 108,367.

Starting with the electrodes in contact with the surfaces of the element or crystal, the frequency ofthe crystal decreases to a certain minimum and then increases as the air gap 1sA lncreased to approximately one tenth thetliickness of the-crystal when the crystal stops oscillating. The actual length of the air. gap at which oscillation of the crystal ceases is dependent upon the ratio of the velocity of sound in quartz and in air. This ratio varies with the temperature and slightly with different crystals. It also depends somewhat on the way in which the element is cut from the crystal.

The activity of the oscillator slab through thesame range of adjustment of the air gaps starts off rather feebly when in contact, and increases rapidly reaching a maximum when the air gap is approximately one fifteenth the thickness of the oscillator slab. With a further increase in the air gap, the activity of the crystal rapidly decreases and ceases to lation of the reflected compression wave in` the air -gap and that in the oscillator slab. When the electrodes are nearly in Contact with the oscillator slab, the reflected compression wave in the air gap is nearly 180 degrees out of phase with the compression wave in the oscillator slab and is assisting. f

When the air gap is approximately one fifteenth the thickness of the oscillator slab Y the compression wave is in phase and them amplitude of the oscillator slab is a maximum, consequently its output is a maximum. As the air gap is further increased the relected compression wave in the air gap becomes more and more 'out of phase until when one tenth the thickness of the oscillator slab it is 180 degrees out of phase, and in direct opposition, and therefore reduces amplitude o the oscillator slab to the point where it prevents any but the most extraordinary crystals from oscillating. In accordance with my invention; proper operation of the element is produced by means of a construction wherein the spaci between the electrodes is readily adjuste and wherein the electrodes are securel fixed or mechanically locked to ther wit any desired spacing between t em. j

My invention will be better understood from the following description when considered in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

'Referring to the drawings, Figs. 1 to 4 shows various views of a piezo-electric oscillator constructed in accordance with m invention; and Fig. 5 shows a modifie arrangement for locking the electrodes together when the spacing between them has een adjusted.

Figs. 1 to 4 show electrodes 1 and 2 which are mounted on an insulation base 3, are connected to the plug terminals 4 and 5 respectively and are surrounded by an insulation cover 6 which is removably attached to the insulation base 3 and is provided for protecting the electrodes against temperature changes. It should be noted that the electrode 2 is attached to the insulation base 3 by means of screws 7, that the adjustable electrode l is threaded into a support member 8 which is attached to the insulation base 3 by means of screws 9, that the insulation cover 6 is attached to the base 3 by means of screws 10, and that a cylinder 11 of some resilient material such as Celluloid, hard rubber, or bakelite, is mounted within the support or wall member 8 to act as a shock absorber for the piezo-electric element, which is normally supported between the electrodes 1 and 2.

The manner in which the electrodel is locked in an osition to which it has been adjusted wil readily understood upon consideration of Figs. 3 and 4. As indicated by these igures, the wall or support member 8 is threaded on its inner periphery to it the edge of the electrode 1 loosely and is thereafter deformed at points 12, 13 and 14 so that the adjustable electrode 1 .will not quite thread into it. In order to permit adjustment of the electrode 1 along the threaded part of wall member 8, an adjustment rin 15 is provided. This ring is provided wit projections 17 and 18 at its inner periphery and with a thumb-screw 19 which is spaced from these projections and extends through the inner periphery of the rin hen it is desired to adjust the electrode 1, the adjustment ring 15 is so positioned around the deformed wall member 8 that the points of eatest deformation toward the center of t e rin are between the projections 17 and 18. he thumb-screw 19 is then tightened against the outer wall of the member 8, thus restoring this member to a substantially circular form and permitting ready adjustment of the electrode 1. Upon removal of the ad'ustment ring the wall member 12 tightly inds'the electrode 1 at the points 12, 13 and 14, thereby securely locking it in the position to which it has been adjusted.

Fig. 5 shows an adjustable electrode 1 provided with a flan 20 throughV which jamb screws 21 are t eaded for the purpose of locking the electrode in any position to which it is adjusted.

It will be apparent that the locking arrangement shown b Figs. 3 and 4 differs from that shown by Fig. 5 in that there is no visible means of adjustment when the adjustment ring has been removed. This feature is of advantage in that it makes it impossible for anyone who is unfamiliar with the construction to tamper with the adjustment. The insulation casing 6 not only protects the oscillator from dirt and moisture, but also prevents change in the spacing between the electrodes due to sudden changes in temperature.

The form of the invention shown by Fi 1 to 4 of this application is specificasj7 claimed in an application of Alexander J. R. Fiego, Serial No. 102,342, filed April 15,1926, and assigned to the same assignee as the present application.

The embodiments of the invention illustrated and described herein have been selected for. the purpose of clearly setting forth the principles involved. It will be apparent however, that the invention is susceptible o being modified to meet the different conditions encountered in its use, and I therefore aim to cover by the appended claims all modiiications within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is 1. A piezo-electric oscillator comprising a pair of electrodes electrically insulated from one another, and a threaded connection operable to adjust the electrode spacing and means for locking said electrodes together with any desired spacing therebetween.

2. A piezo-electric oscillator comprising a pair of electrodes electrically. insulated from one another, a threaded connection operable to adjust the electrode spacing means for locking said electrodes together with any desired spacing therebetween, and a casing surrounding said electrodes and connection.

3. A piezo-electric oscillator comprising a pair of electrodes electrically insulated from one another, a mechanical connection operable to adjust the electrode spacing means for locking said electrodes together with any desired spacing therebetween, a casing sur rounding sai electrodes and connection, and terminals extending through one side of said casing for connectmg said electrodes to an external circuit.

4;. A piezo-electric device com rising a pair of electrodes electrically ated and mechanically spaced from one another. a sup port attached to one of said electrodesa a threaded connection between said' support and the other of said electrodes :for adiusting the spacing between said electrodes, and means for locking said connection to 1erea vent change in the adjustment oii the electrode spacing.

5. A piezo-electric device com rising a pair of electrodes electrically insu ated and mechanically spaced :from one another, a support attached to one of said electrodes., a threaded connection between said support and the second electrode Jfor adjusting the spacing between said electrodes, and a .screw threaded throu h the edge o the second electrode for loc ing said connection to re vent change in the adjustment of the e ec trode spacing. i

6. A piezo-electric oscillator comprising a pair of electrodes electrically insulated from one another, a mechanical connection opera ble to adjust the electrode spacing2 means for locking said electrodes together with any sired spacing therebetween, and a resilient collar adjacent the inner periphery of said connection.

In witness whereof, I have hereunto set my hand this 7th da of Ma 1926.

ALJARAD L. R. ELLIS. 

